It should work across of browsers.
I tried .onreadystatechange in IE, however it seems not reliable. Other recommendation are based on setting time out thread which monitors some value which supposed to be set by a script from a loaded page. Unfortunately, my users have attachments with size from 1MB to 8GB, so upload time is varying from 3 seconds to 1 hour and putting 30 minutes time out isn't a solution. Any other ideas? Pinging server using xmlhppt?